A: Primary aliphatic amines react with `CS_(2)` and `HgCl_(2)` give precipitate of Hgs.
R: Secondary amine does not give precipitate of Hgs in this reaction.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) step by step.

### Step 1: Understanding the Assertion (A)
The assertion states that primary aliphatic amines react with carbon disulfide (CS2) and mercury(II) chloride (HgCl2) to give a precipitate of mercury sulfide (HgS).

- **Reaction Mechanism**:
1. A primary aliphatic amine (RNH2) reacts with carbon disulfide (CS2).
2. The lone pair of electrons on the nitrogen atom attacks the carbon in CS2, leading to the formation of dithioalkylcarbamic acid.
3. This compound then reacts with HgCl2 to form alkyl isothiocyanate and precipitate HgS.

### Step 2: Understanding the Reason (R)
The reason states that secondary amines do not give a precipitate of HgS in this reaction.

- **Why Secondary Amines Do Not React**:
1. Secondary amines (R2NH) lack the necessary reactivity to undergo the same reaction with CS2 as primary amines.
2. The reaction mechanism is specific to primary amines due to the presence of a hydrogen atom attached to the nitrogen, which is essential for the formation of the intermediate that leads to HgS precipitation.

### Step 3: Conclusion
Both the assertion and the reason are true:
- The assertion is true because primary aliphatic amines do indeed react with CS2 and HgCl2 to form HgS.
- The reason is also true, as secondary amines do not participate in this reaction.

However, the reason provided does not correctly explain why the assertion is true, as it simply states that secondary amines do not react without explaining the underlying mechanism.

### Final Answer
Both the assertion and the reason are true, but the reason is not the correct explanation for the assertion. Therefore, the correct answer is option 2.

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